A carbureted internal combustion engine employs an intake manifold to distribute a fuel and an air mixture produced by a carburetor to the cylinders of the engine. An intake manifold typically has a plenum chamber below the carburetor to receive a mixture of fuel and air from the carburetor. From the plenum, the mixture is directed to the cylinders through ducts called runners or tracts. The tracts exit from the manifold at inlet ports to the engine. These ports lead to the cylinders through inlet valves.
Reversion disrupts induction, which is the aspiration of the intake charge into and through the intake tract, and therefore prevents the delivery of the proper mix of fuel and air to the combustion chamber in response to changes in throttle and power demand. Reversion refers to the movement of exhaust gases in the reverse direction, backing up through the intake flow path. That effect essentially robs the engine of power that would otherwise be available from the charge of fuel. It is appreciated that internal combustion engines are designed to move gasoline vapors in one direction, through the intake as an air-fuel mixture, into the combustion chamber and, following combustion, from the combustion chamber as exhaust gases out the exhaust port. When instead exhaust gas reenters the intake tract and pollutes the air-fuel mixture, the nature of the combustible mixture is altered. The potential power of combustion that would otherwise be obtained from the fuel in the internal combustion process is reduced.
Reversion is the reverse or back flow of a portion of the intake charge through an intake tract of an engine as a result of a pattern or series of reverse or upstream traveling shock waves or pulses that enter the intake tract when the intake valve is open. These shock waves or pulses are the result of the high pressure developed by combustion in the combustion chamber, and also back pressure from the exhaust, both of which can be transmitted to the intake tract through an open intake valve, thereby contaminating the intake charge.
Reversion has been observed to move mainly through the stagnant or dead spaces in the intake tract where the intake flow has little or no velocity, and more importantly, along the wall of the intake tract in essentially the boundary layer of the intake charge flow stream. The upstream traveling pulses and back pressure cause some of the adjacent downstream traveling intake charge flow to be slowed, stalled, or even reversed. The upstream traveling pulses and back pressure tend to decrease or dilute the intake vacuum signal. A decreased vacuum signal represents a corresponding drop in induction as well as a resultant loss in engine responsiveness and smoothness.
Consider the operation of one cylinder in a four stroke internal combustion engine. In a first (or intake) stroke, the intake valve opens and the piston is moved downwardly, creating a low pressure, relative to atmospheric pressure, in the combustion chamber above the piston head. Consequently, air flows through the intake manifold, a conduit connected to the carburetor, from the high pressure of the ambient atmosphere to the lower pressure in the engine. The air passes through the carburetor, drawing gasoline droplets out from the carburetor""s metering rod, which regulates the flow rate of gasoline drawn into the airstream, creating an air and fuel mixture of the proper proportion for efficient combustion. The mixture is drawn into the cylinder head""s intake port and, with the intake valve opening, into the combustion chamber.
In the second (or compression) stroke, the intake valve closes and the piston moves upward, thereby compressing the fuel and air mixture within the combustion chamber. Near the end of the piston""s upward stroke, the spark plug is ignited, igniting the compressed mixture and creating an explosion in the confined volume. The more completely the gasoline droplets are vaporized during the compression cycle, the more efficiently the engine produces work from the gasoline fuel. The smaller the gasoline droplets, the more fully they will vaporize during the compression stroke. Larger, unignited gasoline particles or droplets which result from inefficient carburetion represent wasted energy.
The force created by the expanding gases in the explosion drives the piston downward, the third (or power) stroke in the cycle; in turn, the piston rotates the engine""s crankshaft, producing work. During the fourth (or exhaust) stroke, the exhaust portion of the cycle, the exhaust valve opens the exhaust port. The piston moves upward and forces the exhaust gases, the products of combustion, out the exhaust port. Due to the high pressure created in the chamber, the exhaust gases flow out of the combustion chamber of the cylinder and through the engine""s exhaust pipe, ultimately exiting to the atmosphere. The foregoing cycle repeats.
The points at which the valves open and close during the cycle is typically determined by the lobes on a camshaft, which in turn are synchronized to the rotation of the crankshaft driven by the pistons. The point in the cycle at which the spark plug is ignited is synchronized to the rotation of that same crankshaft.
During the intake stroke, when the intake valve is open and the piston moves downward, the air and fuel mixture is drawn into the combustion chamber. During the exhaust stoke, when the piston moves upward, the exhaust gases are forced through the open exhaust valve. At the end of the exhaust stroke of one cycle and the beginning of the intake stroke of the next cycle, the intake valve starts to open even though the exhaust valve has not fully closed. This is the point in the cycle referred to as a period of xe2x80x9cvalve overlap.xe2x80x9d It is at this point in the cycle of operation in which reversion, i.e. movement of exhaust gases back up through the intake flow path, occurs. Importantly, reversion causes exhaust gases to pollute and dilute the clean air-fuel mixtures, thereby dramatically altering the nature of the combustible mixture and reducing the potential power that would otherwise be obtained from the fuel in the mixture. As those skilled in the art recognize, valve overlap is a necessary and unavoidable condition inherent in the four stroke engine cycle.
During valve overlap, the different pressure levels present in the intake and exhaust paths are exposed to one another through the combustion chamber. The intake path is closer to the atmosphere and is a lower pressure area. The exhaust gases are at a higher pressure created by the fourth stroke in the cycle and hot expanding gases. The exhaust gas naturally flows to the lower pressure region of the inlet. Because exhaust gases have not been completely evacuated from the combustion chamber and because the intake flow of air-fuel mixture to the combustion chamber is constrained by the opposing flow of exhaust gases, the ultimate result is that the engine develops less power than it otherwise could, an effective loss of power.
Reversion is usually even more problematic in two stroke internal combustion engines than in four stroke engines because of several reasons. First, two stroke engines operate at higher speeds than four stroke engines. Additionally, two stroke engines lack a separate intake stroke compared to four stroke engines; therefore, the intake valve is open more frequently than in a four stroke engine. Reversion is also a problem in virtually any engine when operating under heavy load conditions such as while powering a vehicle in a climb. Reversion has been found to be so great in some engines, particularly two stroke engines, that the engines will not operate without means to reduce or contain the reversion.
Known constructions effective for reducing or containing reversion include devices known as reversion traps, usually located in the intake passage, and reversion tubes, usually located in the exhaust passage. Reversion traps generally include a restriction or neck in the exhaust passage upstream of a larger expansion area or chamber. The restriction or neck traps or limits the back flow of pressure and contaminants through the conduit. Reversion tubes operate generally in the same manner as reversion traps, but in the intake passage. Shortcomings of both devices include that they do little or nothing to improve intake charge atomization and vaporization and are not designed to recapture and put to useful work the energy of the reverse pulses or back pressure.
There is a need for a device which not only reduces the negative effects of reversion but also uses reversion for productive work, thus making the engine more efficient. It is known that to the extent an engine can be made more efficient, the engine will be more economical to run. Such efficiency also can also lead to the reduction of harmful exhaust emissions.
The present invention is an apparatus for redirecting a reversion pulse between a combustion chamber of an internal combustion engine and a fuel and air mixing device. The apparatus comprises a helical pathway through which a charge traveling from the fuel and air mixing device to the combustion chamber flows. The apparatus further comprises a chamber disposed at a periphery of the helical pathway. A reversion pulse traveling from the combustion chamber to the fuel and air mixing device flows into the chamber.